1. Field of the Invention
Embodiments of the present invention relate generally to a printed circuit board and a method of manufacturing a printed circuit board. In one aspect, the present invention relates to a printed circuit board having a high density of circuit components, some of which are suitable for use as surface mounted components. In another aspect, the present invention relates to a method of manufacturing a printed circuit board having a high density of circuit components.
2. Description of Related Art
Conventional methods of mounting circuit components on a printed wiring board include a "through-hole" technique which involves extending leads, commonly called "posts", of a circuit component through the printed wiring board and then soldering in place. The posts electrically connect circuit paths embedded on or within the board.
Another mounting method, called "Surface Mount Technology" (SMT), involves initially placing circuit components onto circuit paths embedded on the upper surface of the printed wiring board and then soldering the component in place by a process called "reflow soldering". Common surface mount components utilize connector leads commonly referred to as "J-leads" or "gull-wings" which rest on the surface of the printed wiring board rather than penetrate through it as with the through-hole technique.
SMT increases the density of circuit components on a printed wiring board by enabling the use of smaller components which are arranged in a flat configuration on the surface of the board. In such surface mounted components, the leads to be surface mounted may be tightly spaced, as compared to components mounted by the through-hole technique, enabling more I/Os per unit area of the component. SMT requires less printed wiring board space due to increased packaging density, thus lowering the cost of the entire system. SMT is also less costly due to the elimination of the drilling procedure associated with conventional through-hole mounting methods. Also, many surface mounted components may be soldered in place at the same time using reflow soldering.
In the past, efforts to increase the density of printed circuit boards have included the mounting of circuit components within depressions or wells etched into the printed circuit board. See, for example, Ilardi et al. U.S. Pat. No. 4,999,740. Efforts to orient circuit components on a printed circuit board include the mounting of circuit components within or above openings etched through the printed circuit board. See, for example, IBM Technical Disclosure Bulletin, September, 1981; Kobayashi Japanese Patent 30,439; Harada et al. U.S. Pat. No. 4,631,820; Inoue German Patent No. 3,739,985; Cnyrim et al. U.S. Pat. No. 4,959,750. Still other efforts to orient circuit components on a printed circuit board include the mounting of two circuit boards together, see for example Igarashi U.S. Pat. No. 4,742,431, the mounting of circuit components within a socket which is then mounted to the printed circuit board, see for example, Tonooka U.S. Pat. No. 4,883,428, or the housing of circuit components within an inductor structure, see for example Chason et al. U.S. Pat. No. 5,083,236.
High density printed circuit boards create greater utility in a smaller electronic device. Increasing the density of circuit components on a printed circuit board, however, often results in overheating of the components leading to eventual burnout and replacement of the components. The resulting overheating can also cause higher stress and strain in the interconnects, such as solder joints, leading to an early failure. The need to increase density while reducing repairwork is necessary to make further advances in the efficiency and reliability of smaller electronic devices.
Unfortunately, prior efforts (1) fail to maximize the density of circuit components on a printed circuit board and (2) fail to increase density in a manner which reduces repairwork associated with the devices incorporating the printed circuit boards. A need therefore exists to develop a printed circuit board which maximizes density of circuit components while reducing repairwork, thus leading to smaller, more efficient and reliable electronic devices.